Titania nanotube arrays have been fabricated on a fluoride-doped tin oxide substrate by liquid phase deposition using ZnO nanorod arrays as a template and have been applied as the electrode for dye-sensitized solar cells (DSCs). The performance of DSCs based on TiO2 nanotube electrodes can be improved by treating the TiO2 nanotube arrays with titanium tetrachloride (TiCl4) . Both the short-circuit current density and the conversion efficiency increased almost 2 times after the TiCl4 treatment. The TiCl4 treatment not only increased the amount of absorbed dyes but also enhanced the electron transport in the TiO2 films. TiCl4 -treated TiO2 nanotube arrays with 4μm thickness showed a short-circuit current density of 8.37mA/cm2 , an open-circuit voltage of 0.80 V, a fill factor of 0.67, and an overall conversion efficiency (η) of 4.53%.
ZnO nanorods and nanoparticle electrodes have been applied to solar cells possessing characteristics of bulk heterojunction and dye-sensitized devices. First, the ZnO electrodes were covered with fullerene acid molecules to yield the monolayer on the electrodes. Then, zinc porphyrin and fullerene acid molecules were spin coated onto the modified surfaces to give porphyrin−fullerene-modified ZnO electrodes. The porphyrin−fullerene-modified ZnO nanorod devices with the intervening fullerene monolayer exhibited efficient photocurrent generation compared to that of the reference systems without the fullerene monolayer. The significant improvement of the photocurrent generation efficiency by the fullerene monolayer may be associated with efficient charge separation in the porphyrin−fullerene composite layer, followed by electron injection into a conduction band of the ZnO nanorod electrode together with the suppression of charge recombination between the separated charges by the fullerene monolayer. Cell performance was optimized by altering the length and diameter of the ZnO nanorods and density of the ZnO nanorod array. The effects of the ZnO electrode structures (i.e., nanorod versus nanoparticle) on the photoelectrochemical properties were also compared under the same conditions. Despite a larger surface area of the ZnO nanoparticle electrode by a factor of 3 compared with that of the ZnO nanorod electrode, we noted similar photocurrent generation efficiencies. This can be rationalized by the facts that only the top surface of the porous ZnO nanoparticle electrode is covered by the porphyrin−fullerene composite layers, whereas the entire surface of the ZnO nanorod electrode is wrapped in the composite layers. The photocurrent generation mechanism was also corroborated by steady-state fluorescence and fluorescence lifetime measurements. The results obtained from this study will provide basic and valuable information on the design of electrode structures and the donor−acceptor combination toward the improvement of cell performance in dye-sensitized bulk heterojunction solar cells.
Oilfield formation damage by scale formation can occur when two incompatible brine streams are mixed. A common method for preventing scale formation is the use of chemical scale inhibitors such as aminotri-(methylene phosphonic acid) (ATMP). Scale inhibitors are injected and retained in the reservoir by adsorption and/ or precipitation. The induction time, the period between the establishment of supersaturation and the detection of a new phase, is a measure of the ability of an inhibitor solution to remain in the metastable state. As a result, long induction times allow transport of inhibitor fluids into the near-wellbore regions without precipitation of the scale inhibitor and subsequent formation damage. In this study, an induction time model is applied to precipitation of the inhibitor (ATMP) with Ca 2+ ions. The nucleation kinetics can be described by classical nucleation theory. Solution equilibrium was calculated by accounting for inhibitor dissociation and cation-inhibitor complexing as a function of ionic strength. Conditions such as the initial concentration of inhibitor, the solution pH, and the presence of soluble impurities significantly impact the precipitation kinetics of inhibitors. Long induction times were observed at low initial concentrations of inhibitor, at low values of the solution pH, and in the presence of impurities. Monovalent cation impurities (Li, Na, and K) inhibit the nucleation of Ca-ATMP to the same extent, indicating there is no effect on the different types of monovalent cations. Divalent cation impurities inhibit the nucleation of Ca-ATMP more than monovalent cations, and different divalent cations have different induction times. The reduction of nucleation rate is a result of increasing the surface free energy. This study provides an understanding of scale inhibitor precipitation kinetics which will be beneficial for delaying inhibitor precipitation in order to avoid reservoir permeability problems in near-wellbore region.
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